1. Field of the Invention
The present invention relates to a tape cassette provided with a locking member for locking hubs contained therein while the tape cassette is not in use.
2. Description of the Prior Art
Some practical tape cassettes holding a tape for the high-density recording of video signals or PCM signals, such as 1/2 in. video tape cassettes and 8 mm video tape cassettes, are provided with a locking member for locking hubs contained therein while the tape cassettes are not in use and kept for storage. Such a locking member is pressed by the resilience of a spring against the hubs to lock the hubs when the tape cassette is not in use. The locking member is separated from the hubs by an unlocking pin to unlock the hubs when the tape cassette is inserted in a tape drive. Such tape cassettes provided with a locking member are disclosed, for example, in U.S. patent application Ser. Nos. 622,649 filed Dec. 5, 1990, 802,405 filed Dec. 4, 1991 and 827,933 filed Jan. 29, 1992.
FIGS. 1a and 1b are a schematic plan view and a schematic side view, respectively, of a prior art tape cassette in an inoperative state, and FIGS. 2a and 2b are a schematic plan view and a schematic side view, respectively, of the same prior art tape cassette in an operating state, in which indicated at 61 is a locking member, at 62 are hubs, at 63 indicated by alternate long and short dash lines is the case body 63 of the tape cassette and at T is a tape held on the hubs 62.
The locking member 61 is provided with locking protrusions 61a which engage teeth 62a formed in the circumferences of the hubs 62 to lock the hubs 62 and has the shape of a substantially T-shaped flat plate. A locking spring 61c, such as a stainless steel spring wire, has opposite ends connected to knuckles 61b.sub.1 and 61b.sub.2, and a middle portion engaging a peg 64 formed on the inner surface of the case body 63. Normally, namely, when the tape cassette is not in use, the locking member is biased toward the hubs 62 by the locking spring 61c so that the locking protrusions 61a engage the teeth 62a to lock the hubs 62 as best shown in FIG. 1a.
When the tape cassette is inserted in a recording/reproducing apparatus, an unlocking pin 65 enters the tape cassette through an opening 63a formed in the case body 63 and engages the edge 61d of the locking member 61 provided with flat slopes 61d.sub.1 and 61d.sub.2 at a position corresponding to the opening 63a to push the locking member 61 up against the resilience of the locking spring 61c as shown in FIG. 2b, so that the locking protrusions 61a are disengaged from the teeth 62a to unlock the hubs 62 as shown in FIG. 2a. The locking member 61 is provided with a slot 61f and a guide pin 66 formed on the inner surface of the case body 63 is fitted in the slot 61f to guide the locking member 61 for sliding movement between a locked position shown in FIG. 1a and an unlocked position shown in FIG. 2a.
When pushed by the unlocking pin 65, the locking member 61 slides in a space between the hubs 62 along the inner surface of one of the halves of the case body 63. Since the locking member 61 has the shape of a flat plate and is in close contact with the inner surface of the half of the case body 63, it occurs, in some cases, that the locking member 61 is unable to slide smoothly. It is possible to avoid plane contact between the locking member 61 and the inner surface of the half case of the case body 63 to ensure the smooth sliding movement of the locking member 61 by forming ribs parallel to the direction of movement of the locking member 61 on the inner surface of the half of the case body 63 and making the locking member 61 slide along the ribs. However, the locking member 61 is liable to be supported on the ribs within the case body 63 of the tape cassette in an unstable position and unable to lock the hubs 62 properly.
In such a prior art hub locking arrangement, the unlocking pin 65 slides along the flat slope 61d.sub.1 (61d.sub.2) to push the locking member 61 against the resilience of the locking spring 61c and a considerably large force is exerted on the point of contact between the flat slope 61d.sub.1 (61d.sub.2) and the extremity of the unlocking pin 65, which hinders the entrance of the unlocking pin into the tape cassette and abrades the flat slope 61d.sub.1 ( 61d.sub.2).